Many solid state devices, such as diodes, transistors and the like, are encapsulated in a hermetically sealed housing. One type of such a housing includes a metal header on which the solid state device is mounted, and a metal cup-shaped cap fitting over the header and the solid state device and welded to the header. The cap generally includes a flange extending radially outwardly from the rim of the cap and having a weld ring projecting from the surface of the flange toward the header. The cap is mounted on the header by placing the flange over the surface of the header with the weld ring contacting the surface of the header. Welding electrodes are placed on opposite sides of the cap flange and header, and the flange and header are squeezed between the electrodes as a current is provided therethrough. The current causes the weld ring to heat up so that the weld ring melts and under the pressure applied by the electrodes welds to the header. This forms a hermetic seal between the flange of the cap and the header.
A problem with this type of welded structure is that the heating of the weld ring to form the weld also results in the formation of an uncontrolled splashing of small metal particles which become trapped in the housing. These particles can interfere with the proper operation of the solid state device in that they can cause particle induced noise. Although testing for particle induced noise was once required only for high reliability solid state devices, it has more recently been a complaint by many other users of the solid state devices. Therefore, it would be desirable to have a welded metal housing which minimizes, if not eliminates, the metal particles so as to greatly reduce the particle induced noise problem.